Question

A body travels 200 cm in the first two seconds and 220 cm in the next four seconds. The velocity at the end of seventh second from start is

• A. 5 cm/s
• B. 10 cm/s
• C. 15 cm/s
• D. 20 cm/s

Answer 1

The correct option is B

10 cm/s

Case II :

Body travels 220 cm in next 4 seconds

We know,
$s_2=u{t}_2+\frac{1}{2}a{t}_2^2$

Putting all the values
$\Rightarrow 420=u\times 6+\frac{1}{2}a\times 6^2$
$\Rightarrow$ 420=6u+18a
$\Rightarrow$ u+3a=70 …(2)

Now,
Solving (1) and (2), we get
$a=-15m/s^2$
and u = 115 cm/s.

From the equation of motion

We know,
v = u + at

Or,

V = 115 - 15 $\times$ 7 = 10 cm/s.

Hence the speed at the end of seventh second is 10 cm/s